Users of mobile stations find the opening of the keypad lock to be problematic, especially in conditions with a restricted level of lighting. In some manufacturers terminal equipment, if the keypad is in the locked state, a random keystroke will not activate the illumination of the keypad and the display, which instead requires the correct keys to be pressed in the correct sequence and results in both the illumination being activated and the keypad lock being opened.
A second alternative is to activate the keypad illumination by pressing the mobile station's power switch (Power On/Off key). From the viewpoint of the mobile station's user, the operation nevertheless takes a painfully long time in both cases, thus creating a usability problem.
Recently, mobile stations with entirely new keypad configurations have appeared on the market. In them, the arrangement of the keys is very different to the accustomed matrix configuration. In the new models, the keypad can be arranged, for example, in the form of a circle, or may be divided into two parts, which are divided, for example, by the display component. Users who are unfamiliar with the new keypad arrangements may find difficulty in forming an image of them, for example, in conditions with restricted lighting.
Further, the prior art discloses an user interface feature for visualizing a locked keypad, implemented by one terminal-equipment manufacturer. In this case, pressing any key at all in the keypad activates the illumination of the terminal equipment, which can be observed to be at full power and to cover the whole keypad component. The illumination can then last for 15–30 seconds, for instance. Similarly, the entire display component of the terminal equipment can also be observed to be illuminated at full power and is used to display an indicator effect for opening the keypad locking.
In this case, the terminal equipment quite obviously wakes from sleep mode and switches to stand-by mode. Switching to stand-by mode has, as is known, a significant effect on power consumption, particularly in portable terminal equipment.
Besides such visualization showing the location of the input and display components being performed only when the user knowingly presses some key, the visualization also takes place in several other situations without the knowledge of the user. Such situations arise, for example, when the terminal equipment is in the user's pocket or correspondingly in a terminal-equipment holder attached to their belt, where the keys may be pressed unintentionally. It is fairly obvious that all such intentional and unintentional activations will significantly affect the overall power consumption of the terminal equipment.
As the prior art of the keypad locking is also referred to the publications EP-0 453 089 B1 and EP-0 590 494 A1.